


Tell Me

by hyliank8



Series: Sanster Experiment AU Collection [3]
Category: Undertale (Video Game)
Genre: Alternate Universe - Vampire, Angst, Begging, Blood Drinking, Evil W. D. Gaster, Helplessness, Hurt No Comfort, M/M, Magic Blood, Manipulation, Sanster Experiment AU, Stockholm Syndrome, Vampire Gaster AU, Vampire W. D. Gaster, W. D. Gaster is not related to Skelebros, experiment au
Language: English
Status: Completed
Published: 2020-09-13
Updated: 2020-09-13
Packaged: 2021-03-06 20:40:09
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 1
Words: 1,288
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26435050
Author URL: https://archiveofourown.org/users/hyliank8/pseuds/hyliank8
Summary: Gaster is a vampire who uses his experiment both as a food source and as a means to sate his twisted desires.S-01 always serves his purpose, whether he wants to or not.(Vampire Gaster AU + Sanster Experiment AU)
Relationships: W. D. Gaster/Sans
Series: Sanster Experiment AU Collection [3]
Series URL: https://archiveofourown.org/series/1905070
Comments: 10
Kudos: 47





	Tell Me

**Author's Note:**

> ok so i like the vampire gaster au and i like this sanster experiment au so,,,, obviously the next logical step was,,,,,,, mash them together???? but like, painfully, of course. poor sans.
> 
> enjoy :p

S-01 desperately tries to focus on the warmth of his creator’s body as every thrust from the larger monster rocks him further into the uncomfortably thin mattress. He squeezes his eyes shut, trying to think about the way Gaster’s heat shields him from the frigid air in his cell... as though the doctor is protecting him from the cold, keeping him safe.

As though Gaster cares about him, cares about his comfort.

S-01 fearfully tightens his grip on the back of Gaster’s lab coat, shivering as his creator’s sharp teeth scrape threateningly against his fragile vertebrae. 

_no, no... not now, please..._ It’s been hard to perform well during Gaster’s rather thorough mental examinations, and S-01 knows the extra difficulty is a direct result of how often Gaster’s been drinking from him lately. A feeding session always leaves S-01 feeling drained for days afterward, and it’s surely been weeks since he’s had the luxury of a break.

But the searing pain of his creator’s unforgiving teeth sinking into his neck doesn’t come—S-01 only feels a grin stretch across Gaster’s face as he revels in his prey’s involuntary shiver.

“Stars, you’re so tight...” Gaster’s voice is a husky whisper, his breath hot on S-01’s neck as the pace of his hips’ movement turns slower. S-01 whimpers as the decreased speed allows Gaster to thrust deeper inside of him, sending sparks of heat down his spine. The warmth is horribly unpleasant, but he continues desperately trying to convince himself that it’s not so bad—it’s better than Gaster leaving him all alone, right? The room is cold, and he’s sure he’d be shivering uncontrollably without the heat that Gaster’s presence provides. He’d rather be close to him like this than be alone.

And if it’s a little bit _too_ hot, a little bit _too_ close... that’s fine. He can handle it, really. He can take it.

“So warm and wet, too... you’re perfect for me, you know that?”

S-01 doesn’t know how to reply; he never knows what to say when the doctor talks like that. It’s never clear what the right answer is—it’s not like his mental exams where there’s a single correct response every time. Sometimes Gaster wants an answer from him, sometimes he wants him to stay silent. Even under the looming threat of punishment for a mistake, S-01 can’t figure out the pattern.

“y-yes, sir,” S-01 says, hesitantly.

“Mm... you want this, don’t you, S-01?”

 _stars, please, no._ S-01 knows he’s not talking about the sex anymore. He’s not asking him whether he wants Gaster’s hands to keep gripping his wrists so hard he’s sure they’re bruising, he’s not asking him whether he wants Gaster to keep fucking him so forcefully that his soul shivers with every harsh thrust. 

He’s talking about something far, far worse. 

_i don’t, i don’t want this, please don’t do this now_ —S-01 is still so weak from the last time, he’s sure he’ll end up too drained to walk for _days_ if Gaster feeds from him again.

He almost wants to beg aloud, but he knows that would be useless.

“You want me to take your magic, you _want_ to give it to me,” Gaster continues, clearly unconcerned with S-01’s silence. “...Because you don’t have a purpose otherwise, do you?”

S-01 can’t find his words. He’s terrified; he hoped after the rough experiments today that maybe the doctor would give him a break, would let him keep some of his magic to aid in naturally healing himself. But clearly he was wrong, and he trembles in anticipation of the pain—every time Gaster drinks his magic it hurts worse than even the cruelest experiments the doctor performs. It feels like the magic is being ripped from him, torn directly from his soul, and it’s always terrifying and overwhelming all at once.

But as his creator’s words sink in, he realizes that Gaster... isn’t entirely wrong. It’s true; what else is he good for other than serving Gaster? He’d be useless if Gaster didn’t take his magic, and then Gaster wouldn’t want him and he’d be all alone and... S-01 can’t bear the thought of that, can’t bear the thought of Gaster leaving him alone forever.

Gaster is the only thing S-01 has. He’s the only thing S-01 has _ever_ had.

“You’re nothing without me. So sweet, and small... and _pathetic_.” He punctuates his words with a particularly rough thrust that forces a whimper out of the weaker monster.

“...y-yes... yes sir,” S-01 manages, terrified of the consequences of remaining silent for any longer.

“Beg me to take you,” Gaster demands, his voice thick with lust. “Beg me to drink your magic.”

_stars, i don’t want the pain, i don’t want the pain this time, please, please..._

“...pl-please... please take my magic, Doctor.” S-01 has to force the words out, his voice barely a whisper. 

He can’t stop shaking.

“Speak up,” Gaster growls.

~~_“Say it like you mean it,” he’s told S-01 before, and S-01 could barely hear him, the sound of his bones snapping still ringing in his skull and it’s deafening—_ ~~

_i’m sorry, i’m sorry, please don’t..._

“please drink my magic, sir,” S-01 tries again, fear pushing him to speak louder this time. But his voice is still weak, and he casts out in his mind for some way to force himself to want this, to force the words to feel meaningful, to sound convincing for fear of his creator’s retaliation otherwise.

“...please... use me,” S-01 continues. “i want to be useful for you... i want to be g-good for you.”

It’s true. Saying it aloud doesn’t entirely overpower his fear of the pain that he knows will come from his creator forcing his magic out of him, but at least the words come easier; he _does_ want to be good for him, he _does_ want to be useful.

He’ll do anything for Gaster to care about him.

Gaster chuckles darkly. “Of course you do, S-01. Don’t worry; I’ll give you what you want.”

Gaster’s razor-sharp teeth finally pierce S-01’s vertebrae, jarring a weak cry out of the smaller monster. S-01’s soul stutters, pulsing unnaturally as it works to stabilize itself as Gaster begins to drain its magic. Gaster’s tongue slides methodically against his neck, working more blood from the wound left by his teeth.

S-01 can’t help the pathetic sob that escapes him as his soul eventually convulses painfully in response to the unnatural absence of his magic. He grips the back of Gaster’s lab coat tighter, trying to anchor himself amidst the sea of pain, but it only gets worse as Gaster drinks more from him. The pain isn’t new to him at this point; it’s the same every time the doctor feeds on him, but it’s impossible to get used to no matter how many times he experiences it.

S-01 whimpers, still trembling as he feels his magic lowering to dangerous levels. The weaker monster’s instincts urge him to struggle, to pull away, to push the doctor off of him as he continues to drink from him—but years of painful conditioning have taught him better than to listen to his instincts, have taught him better than to defy his creator. It doesn’t matter if he feels that Gaster’s taking too much from him; if he struggles, it will only ever be worse for him.

He has no shortage of scars that can attest to that.

S-01 gasps as Gaster finally pulls away. His soul beats unsteadily, working to re-balance itself with the newfound lack of magic.

Doctor Gaster lets out a relaxed sigh, thirst momentarily satisfied, and licks the excess of S-01’s magic from his sharpened teeth.

“That’s a good boy, S-01,” he murmurs.

**Author's Note:**

> ths was another one of those quick-ish things that was only a wip for a short period of time,,, there's Lots of stuff i'm not happy with but i'm Trying not to let my perfectionism hold up all the ideas i have for all these (wartime, experiment, vampire) sanster AUs :p
> 
> i've been getting so much support for the wartime sanster au from friends, i hope i'll have something up for that one next... 
> 
> come find me on [tumblr](https://hyliantimelordin221b.tumblr.com/) or [twitter](https://twitter.com/K8Maybe) or [elsewhere](https://hyliank8.carrd.co/)! :)
> 
> also i feel like i should say that if you like messed-up sanster, i recommend checking out some of my other fics 😳😳
> 
> if u comment i lov u


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